Mercapto acyl-carnitines and pharmaceutical compositions containing same

ABSTRACT

A novel class of mercapto acyl-carnitines is disclosed, wherein the mercapto acyl radical is the radical of saturated mercapto acids having from 2 to 10 carbon atoms. These mercapto acyl-carnitines are prepared, e.g., by first preparing the corresponding halogen acyl-carnitine and then substituting therein, by nucleophylic substitution, the --SH group for the halogen atom. 
     These mercapto acyl-carnitines are useful therapeutic agents, e.g., for the treatment of intoxications and burns and as mucolytic agents. Dithio diacyl carnitines and hydrochloride salts thereof, which are intermediates, are also disclosed.

The present invention relates to a novel class of carnitine derivatives and, more particularly, to mercapto acyl-carnitines wherein the mercapto acyl radical is the radical of saturated mercapto acids having from 2 to 10 carbon atoms.

The present invention also relates to the processes for the preparation of such mercapto acyl-carnitines and to pharmaceutical compositions containing same.

More specifically, the present invention relates to compounds having general formula: ##STR1## wherein: X⁻ is a pharmacologically acceptable halogenide ion, preferably the chloride ion, and

R is the mercapto acyl radical of a saturated mercapto acid having from 2 to 10 carbon atoms.

This mercapto acyl radical is preferably selected from the group consisting of: mercapto acetyl, 2-mercapto propionyl, 3-mercapto propionyl, 2-mercapto butyryl, 3-mercapto butyryl, 4-mercapto butyryl and 5-mercapto valeryl. Correspondingly, the mercapto acyl carnitines preferred according to this invention are:

mercapto acetyl carnitine halogenide;

2-mercapto propionyl carnitine halogenide;

3-mercapto propionyl carnitine halogenide;

2-mercapto butyryl carnitine halogenide;

3-mercapto butyryl carnitine halogenide;

4-mercapto butyryl carnitine halogenide; and

5-mercapto valeryl carnitine halogenide.

The mercapto acyl-carnitines of formula (I) can be prepared, e.g., by a process comprising the steps of:

(1) reacting carnitine hydrochloride with an halogen acyl chloride in the presence of an organic solvent inert towards the reaction at a temperature comprised between about 30° and about 60° C., thus obtaining the corresponding halogen acyl-carnitine; and

(2) reacting at room temperature the halogen acyl-carnitine of step (1) with a compound selected from the class of alkali metal sulfides and acid sulfides, keeping the pH of the resulting reaction mixture substantially at neutrality by adding an inorganic acid selected between hydrochloric acid and sulfuric acid, thus obtaining the mercapto acyl-carnitine.

In step (1) the organic solvent is preferably trifluoro acetic acid.

In step (2) the compound selected from the class of the alkali metal sulfides and acid sulfides is preferably NaHS.

A preferred process for preparing the mercapto acyl-carnitines of general formula (I) comprises the following steps:

(a) reacting carnitine hydrochloride with an S-protected mercapto acyl halogenide selected among (1) the mercapto acyl halogenides wherein the SH group is protected with either trityl or p-substituted benzyl and (2) the dithio diacyl dihalogenides of formula ##STR2## wherein: X is a halogen atom, preferably chlorine and

R₁ is an alkylene radical having from 1 to 9 carbon atoms,

thus obtaining the corresponding S-protected mercapto acyl carnitine; and

(b) removing by known per se tecniques the protecting group of the S-protected mercapto acyl-carnitine of step (a).

In step (b), when the protective group is either trityl or p-methoxybenzyl, this protective group is removed by acid hydrolysis. When the protective group is p-nitrobenzyl, this group is removed by

(1) converting the nitro group into amino group by hydrogenolysis, e.g. hydrogenating with a Parr hydrogenator at 30-50 psi in the presence of a palladium on carbon catalyst;

(2) treating the S-para amino benzyl derivative thus obtained with the Hopkins reagent and isolating the resulting mercapto acyl-carnitine mercury salt; and

(3) treating the mercury salt thus obtained with H₂ S and isolating the resulting mercapto acyl-carnitine.

When in step (a) L-carnitine hydrochloride is reacted with the dithio diacyl dichloride, the product is a mixture of the corresponding dithio diacyl L-carnitine hydrochloride and dithio diacyl L-dicarnitine hydrochloride. After chromatographic resolution, either the former or the latter compound is converted into the corresponding mercapto acyl-carnitine by reacting it with Zn powder and hydrochloric acid.

Still a further process comprises reacting an acyl carnitine hydrochloride wherein the acyl radical is the radical of an unsaturated organic acid (e.g., crotonic acid) with H₂ S in the presence of a catalyst, e.g., azobisisobutyronitrile, thus obtaining the dithio diacyl dicarnitine hydrochloride which is then reduced with Zn powder and hydrochloric acid.

The following non-limiting examples illustrate the preparation and the chemico-physical characteristics of same compounds according to the present invention.

EXAMPLE 1 Preparation of 3-mercapto propionyl carnitine hydrochloride (V) (see the following reaction scheme) ##STR3## Preparation of 3-bromo propionyl carnitine hydrochloride (IV)

Carnitine hydrochloride(II) (0.01 moles) and 3-bromo propionyl chloride (III)(0.03 moles) were dissolved in an amount of trifluoro acetic acid sufficent to make the resulting reaction mixture homogeneous. The mixture was kept under magnetic stirring at a temperature comprised between 40° and 50° C. (reaction time: 18 hours). The reaction mixture was then cooled to room temperature and slowly poured in Et₂ O (200 ml). The residue which precipitated was washed with some small volumes of Et₂ O, taken up with isopropanol and then precipitated with AcOEt-Et₂ O. The raw residue was crystallized from acetone-methanol.

TLC (CHCl₃, MeOH, NH₄ OH, H₂ O, 55:35:5:5)

Anal. (C₁₀ H₁₉ BrClNO₄)C, H, Cl, N

NMR (D₂ O) δ=2.87 (2H, d, --CH₂ COOH); 3.10-3.33 (11H, m, --N⁺ --(CH₃)₃ and --OCOCH₂ --); 3.50-3.93 (4H, m, ##STR4## and --CH₂ Br); 5.47-5.90 (1H, m, ##STR5##

Nucleophylic substitution of the bromine atom by the --SH group

A saturated solution of NaHS.x H₂ O in 15 cc of 95% ethanol was added very slowly to a solution of 3-bromo propionyl carnitine hydrochloride (3.3 grams; 0.01 moles) in 20 cc of absolute ethanol kept under magnetic stirring at room temperature and under a blanket of gaseous nitrogen. The pH was checked constantly during the addition of the NaHS solution, having care that the pH was kept close to neutrality by HCl addition (even a slightly alkaline pH might cause degradation of bromo propionyl carnitine). The reaction mixture thus obtained was reacted overnight at room temperature. The mixture was then filtered. Upon ethyl ether addition to the filtrate, a precipitate was obtained which was crystallized from isopropanol. The product was kept constantly in an inert atmosphere. NMR analysis showed that this product was the title compound.

Anal. (C₁₀ H₂₀ ClNO₄ S) C, H, Cl, N, S.

NMR (D₂ O) δ=2.80-2.97 (6H, m, --CH₂ COOH, and --OCOCH₂ CH₂ SH); 3.23 (9H, s, N⁺ --(CH₃)₃); 3.70-3.96 (2H, m, ##STR6## 5.47-5.93 (1H, m, ##STR7##

EXAMPLE 2 Preparation of 3-mercapto propionyl carnitine hydrochloride (V) (see the following reaction scheme) ##STR8## Preparation of 3,3' dithio dipropionyl dichloride (VII)

3,3' dithio dipropionic acid (VI) (19 grams; 0.09 moles) was suspended in anhydrous toluene (300 ml.) and thionyl chloride (19 ml.; 0.26 moles) was added to the resulting mixture which was then kept at 90° C. for 20 hours. 18 grams (yield: 77%) of 3,3' dithio dipropionyl dichloride (VII) were obtained which were used as such in the subsequent step.

Preparation of 3,3' dithio dipropionyl L-carnitine hydrochloride (VIII) and preparation of 3,3' dithio dipropionyl L-dicarnitine hydrochloride (IX)

L-carnitine hydrochloride (5 grams; 0.025 moles) was dissolved in trifluoro acetic acid (50 ml.). To the resulting solution the previously prepared dichloride (18 grams; 0.07 moles) was slowly added under stirring. The resulting reaction mixture was kept overnight under stirring at room temperature. The mixture was analyzed by TLC (eluant chloroform, methanol, isopropanol, acetic acid, water 40:40:15:15:10) and was shown to consist of two products having R_(f) 0.3 and R_(f) 0.6, respectively.

Ethyl ether was then added to the mixture and the precipitate which formed was treated with water. The excess of 3,3' dithio dipropionic acid was filtered off and the aqueous solution was lyophilyzed.

The lyophilyzed product was subjected to chromatography on a silica gel column buffered with 1.5% Na₂ HPO₄. Eluant chloroform, methanol 50:50. The product having higher R_(f) (3 grams; yield 30%) [α]_(D) =-27 (C=1, H₂ O) was thus isolated.

NMR analysis showed that the product was 3,3' dithio dipropionyl L-carnitine (VIII). NMR D₂ O δ5.6 (1H, m, ##STR9## 3.8 (2H, m, ##STR10## 3.3 (9H, s, ##STR11## 2.9-2.5 (10H, m, --CH--CH₂ COOH; OCOCH₂ CH₂ S--S--CH₂ CH₂ COOH).

By eluting with methanol, from the same silica-gel column the product having lower R_(f) was isolated. 3.3 grams (yield 30%) were obtained. [α]_(D) =-28. (C=1, H₂ O).

NMR analysis showed that the product was 3,3' dithio dipropionyl L-dicarnitine (IX).

NMR D₂ O δ5.8 (2H, m, ##STR12## 3.8 (4H, m, ##STR13## 3.2 (18H, s, 2 ##STR14## 3.0-2.5 (12H, m, ##STR15##

Conversion of (IX) into (V)

3,3' dithio dipropionyl L-dicarnitine (IX) (1 gram; 0.003 moles) was dissolved in H₂ O (15 ml.) deareated with helium. To the resulting solution, concentrated HCl (1 ml.) and then, portionwise, zinc powder (250 mg.) were added. The resulting mixture was kept under stirring for 15 minutes and then filtered. In order to remove the Zn Cl₂ which formed, the aqueous filtrate was subjected to chromatography by a Chromatospak 100 Jobin Ivon preparative HPLC apparatus.

Resin: Licroprep. RP18, 25-40 mμ, 100 grams

Pressure: 8 atmospheres

Eluant pressure: 6 atmospheres

Flow rate: 25 ml./minute

Eluant: H₂ O-Acetonitrile (degassed with helium) 97:3

Chromatographied product: 1 g/25 ml. H₂ O

The eluted fractions were checked with a Waters model 401 HPLC apparatus.

Resin: μ Bondapak C₁₈

Pressure: 1600 psi

Flow rate: 1 ml./minute

Detector: RI

Chart speed: 0.5 cm/minute.

The fraction containing (V) (R_(f) 6.4) was lyophilyzed away from light and stored under a blanket of Argon. 0.5 grams (yield: 90%) were obtained.

NMR D₂ O δ5.8 (1H, m, ##STR16## 3.8 (2H, m, ##STR17## 3.2 (9H, s, ##STR18## 2.9-2.5 (6H, m, --CH--CH₂ COOH; --OCOCH₂ CH₂ SH).

EXAMPLE 3 Preparation of 3-mercapto butyryl carnitine hydrochloride (X) (see the following reaction scheme) ##STR19## Preparation of 3,3' dithio dibutyryl dicarnitine hydrochloride (XII)

Crotonoyl carnitine hydrochloride (XI) (5 grams; 0.019 moles) was dissolved in ethanol and to the resulting solution catalytic amounts of azobis isobutyronitrile were added. The resulting solution was kept under stirring at 50° C. for 7-10 days and was periodically saturated with H₂ S. Upon reaction termination, the ethanol-containing phase was concentrated and the oily residue thus obtained was repeatedly crystallized from ethanol-ethyl ether. About 5 grams (yield: 42%) of (XII) were obtained.

NMR D₂ O δ5.7 (2H, m, ##STR20## 3.8-3.3 (6H, m, ##STR21## --CH--S--S--CH--); 3.2 (18H, s, ##STR22## 2.9-2.5 (8H, m, ##STR23## 1.3 (6H, m, 2--S--CH--CH₃).

Conversion of (XII) into (X)

(XII) (5 grams; 0.008 moles) obtained in the previous step, was dissolved in 100 cc of degassed H₂ O and 5.5 cc of conc. HCl. To this solution 300 mg. of Zn were added and the resulting mixture was kept under stirring for 0.5 hour under an Argon blanket. The mixture was filtered, the filtrate was lyophilyzed and subjected to chromatography as illustrated in the previous example. 1.5 grams (yield: 63%) of (X) were obtained.

NMR D₂ O δ5.7 (1H, m, ##STR24## 3.8-3.3 (3H, m, ##STR25## --CH--S); 3.2 (9H, s, ##STR26## 2.9-2.5 (4H, m ##STR27## 1.3 (3H, m, --CH--CH₃).

EXAMPLE 4 Preparation of 4-mercapto butyryl carnitine hydrochloride (XIII) (see the following reaction scheme) ##STR28## Preparation of 4,4' dithio dibutyryl dichloride (XV)

4,4' dithio dibutyric acid (XIV) (23.8 grams; 0.1 moles) was suspended in anhydrous toluene (200 cc.) and to the suspension thionyl chloride (35 grams; 0.3 moles) was added. The resulting mixture was kept at the reflux temperature for 4 hours, then concentrated under vacuum, washed with anhydrous toluene and dried. 25 grams (yield: 81%) of (XV) were obtained which were all used as such in the subsequent step.

Preparation of 4,4' dithio dibutyryl L-carnitine hydrochloride (XVI) and of 4,4' dithio dibutyryl L-dicarnitine hydrochloride (XVII)

(II) (6 grams; 0.003 moles) was dissolved in trifluoro acetic acid (50 ml.). To the resulting solution, (XV) (25 grams; 0.09 moles) was slowly added under stirring. The resulting mixture was kept under stirring overnight at room temperature.

The mixture was analyzed to TLC (chloroform, methanol, isopropanol, acetic acid, water 60:40:10:15:15) and was shown to consist of two products having R_(f) 0.2 and R_(f) 0.6 respectively.

To the reaction mixture ethyl ether was added, the precipitate which thus formed was washed with H₂ O, the excess acid was removed and the aqueous solution was lyophilyzed. The lyophilyzed product was subjected to chromatography on a silica-gel column buffered with 1.5% Na₂ HPO₄ (eluant chloroform, methanol 50:100). 2.2 grams of the product at higher R_(f) and 3.5 grams of the product at lower R_(f) were obtained. Product at higher R_(f) [α]_(D) =-26 (C=1, H₂ O).

NMR D₂ O δ5.8 (1H, m, ##STR29## 3.8 (2H, m; ##STR30## 3.2 (9H, s, ##STR31## 2.9-2.3 (10H, m, ##STR32## 2.2-1.6 (4H, m, ##STR33##

NMR analysis showed that this product was the compound (XVI). Product at lower R_(f)

NMR D₂ O δ5.6 (2H, m, ##STR34## 3.8 (4H, m, ##STR35## 3.3 (18H, s, ##STR36## 2.9-2.4 (12H, m, ##STR37## 2.3-1.8 (4H, m, ##STR38##

NMR analysis showed that this product was the compound (XVII).

Conversion of (XVII) into (XIII)

(XVII) (1 gram; 0.002 mole) was dissolved in 15 ml. of H₂ O deareated with helium. To the resulting solution 1.5 ml. of conc. HCl and 700 mg. of Zn powder were added. Zinc addition was carried out slowly and portionwise. The resulting mixture was kept under stirring for about 30 minutes and then filtered. In order to remove ZnCl₂ which formed, the solution was subjected to chromatography at the same conditions as those outlined in Example 3.

The eluted solutions were also checked as indicated in Example 3.

The fraction containing the compound (XIII) (R_(f) 6.46) was lyophilyzed away from light and stored under an Argon blanket.

NMR D₂ O δ5.6 (1H, m, ##STR39## 3.8 (2H, m, ##STR40## 3.3 (9H, s, ##STR41## (6H, m, ##STR42## 2.3-1.9 (2H, m, --CH₂ CH₂ CH₂ SH) [α]_(D) =-25 (c=1 H₂ O)

It has been found that the mercapto acyl-carnitines of formula (I) are useful therapeutic agents for the treatment of intoxications, for the treatment of burns and the diseases of epithelia (and in general whenever it is important to restore to normal the metabolic cellular equilibrium unbalanced by exogenous and endogenous factors) and as mucolytic agents.

It is known that lack of sulphydryl groups SH available for the metabolism requirements, as well as the inability of the organism to utilize such groups in specific pathological situations, constitute the primary factor of anatomical and functional alterations of some body tissues. Indeed, the activity of most of the enzymes present in the cells of vital organs, such as liver, is related to the presence of SH groups in their molecules as well as to the activity of SH groups at the membrane level.

It is also known that the organism, when because of various reasons is unable to utilize the sulphydryl groups indispensable for the cellular metabolism to take place regularly, can utilize the sulphydryl groups that it derives from the administration of compounds containing such groups.

It has been difficult up to now to have available compounds able to cross the biologic membranes and free the SH groups in order to re-constitute the cellular membranes and restore the enzyme activity.

It has now been found that the compounds of the present invention possess a remarkable ability to cross the biologic membranes and particularly the mithocondrial membranes.

Moreover, the mercapto acyl-carnitines provide, in addition to the SH groups, the energy related to the acyl groups (typically, acetyl) which is needed for essential metabolic processes to take place.

The characteristics of pharmacological activity of the compounds of general formula (I) are hereibelow illustrated.

Acute Toxicity

The acute toxicity of the compounds of general formula (I) has been studied in the mouse with the Weil method (Weil C. S., Biometer. J. 8, 249, 1952).

The LD50 values of some compounds illustrated in Table I, indicate that the compounds are remarkably well tolerated. PG,20

                  TABLE I                                                          ______________________________________                                         LD50, mg Kg.sup.-1, ep in mice of some mercapto acyl-carnitines of             general formula (I). Weil's method (N = 5, K = 4) Cl = hydro-                  chloride.                                                                                                         fiducial                                    Compounds          LD50     and    limits                                      ______________________________________                                         mercapto acetyl carnitine Cl                                                                      308             266-350                                     2-mercapto propionyl carnitine Cl                                                                 294             257-345                                     3-mercapto propionyl carnitine Cl                                                                 312             267-357                                     2-mercapto butyryl carnitine Cl                                                                   294             244-294                                     4-mercapto butyryl carnitine Cl                                                                   303             257-349                                     5-mercapto valeryl carnitine Cl                                                                   281             233-328                                     ______________________________________                                    

Protection Against X-Ray Exposure

The effect of the compounds of formula (I) towards the damages provoked by X-ray exposure was studied.

The experiment animals, Albino Wister rats, treated with the compounds under examination (30-40 mg Kg⁻¹ 1 hour before irradiation and 15 mg Kg⁻¹ per day in the subsequent 20 days) were irradiated and checked over a time period to detect the onset of toxic effects and the time of survival with respect to the control group.

In table II, the percentages of survival at the 10th, 15th and 20th day from irradiation are reported.

                  TABLE II                                                         ______________________________________                                         Protective effect of some mercapto acyl-carnitines of                          general formula (I) towards the damage provoked by ir-                         radiation in rats. Percentage of surviving animals at                          various days from irradiation.                                                                    Days of survival                                            Compounds            10       20    30                                         ______________________________________                                         Control              80       20    10                                         mercapto acetyl-carnitine Cl                                                                        85       45    30                                         2-mercapto propionyl carnitine Cl                                                                   80       70    45                                         3-mercapto propionyl carnitine Cl                                                                   90       80    60                                         2-mercapto butyryl carnitine Cl                                                                     100      85    70                                         4-mercapto butyryl carnitine Cl                                                                     100      80    55                                         5-mercapto valeryl carnitine Cl                                                                     95       70    50                                         ______________________________________                                    

Cutaneous Regeneration

The ability of the compounds of formula (I) to speed up the cutaneous regeneration from burns has been tested in rabbits.

A 4 cm² cutaneous area of the average-top zone of the test animal back was burned.

The compounds were orally administered in aqueous solution at the dose of 20 mg Kg⁻¹ once a day for seven days. The area of cutaneous regeneration, i.e. the area of the newly formed tissue was then measured (Table III).

                  TABLE III                                                        ______________________________________                                         Effect of compounds of formula (I) on cutaneous re-                            generation. Percentage of regenerated tissue at the                            4th and 8th day from treatment.                                                                    Days                                                       Compounds             4th day 8th day                                          ______________________________________                                         Control               25      60                                               mercapto acetyl-carnitine Cl                                                                         35      70                                               2-mercapto propionyl carnitine Cl                                                                    30      65                                               3-mercapto propionyl carnitine Cl                                                                    40      80                                               2-mercapto butyryl carnitine Cl                                                                      35      95                                               4-mercapto butyryl carnitine Cl                                                                      25      70                                               5-mercapto valeryl carnitine Cl                                                                      20      60                                               ______________________________________                                    

The expectorant and mucolytic activities of the compounds of formula (I) were determined.

Expectorant Activity

The tests were carried out on male rabbits, weighing 2-3 Kg, anesthetized with ethyl urethane, by following the method disclosed by Perry et al. (J. Pharm. Exp. Ther. 73, 65, 1941).

The anesthetized animals, strapped head downward to an operating table at an inclination of 60°, had a cannula inserted in their trachea. Each cannula was connected to a feeding device which delivered a steady flow-rate of pre-heated air (36°-38° C.) at constant humidity (80%). At the lower end of each cannula, a graduated cylinder was fitted, wherein the bronchial secretion was collected. All of the animals breathed spontaneously and consequently they self-regulated the air intake suitable for normal respiration. After an hour following cannula insertion, the animals were administered orally (by stomach tube) the compounds of general formula (I) dissolved in distilled water at doses comprises between 20 and 40 mg. Each dose of drug was administered to 5 animals. The control animals (8) were given water only. The amount of secretion was determined after 1, 2 and 4 hours from administration. The results, summarized in Table IV, show that the compounds of general formula (I) do not exert expectorant activity.

Mucolytic Activity

The tests were carried out in vitro by using the method disclosed by Morandini et al. (Lotta contro la tubercolosi 47, n. 4, 1977). A thromboelastograph was used to follow the variations induced by the compounds of general formula (I) and acetylcisteine on the rheological properties of human sputum. The results thereof, summarized in Table V, show that the test compounds bring about a greater decrease of human sputum density than that induced by acetylcysteine.

                                      TABLE IV                                     __________________________________________________________________________     Effects of compounds of general formula (I) on bronchial secretion                                          Percentage variations ± s.e. of                                             bronchial secretion versus values at              Number of                    the following intervals after                                                  administration                                    animals                                                                              Treatment              1 hour 2 hours                                                                               4 hours                             __________________________________________________________________________     8     Controls               +0.4   +0.8   +2.1                                5     mercapto acetyl carnitine                                                                       10 mg oral                                                                           +0.3   +0.9   +2.4                                5     2-mercapto propionyl carnitine Cl                                                               10 mg oral                                                                           +0.1   +0.2   +2.0                                5     3-mercapto propionyl carnitine Cl                                                               15 mg oral                                                                           -0.2   +0.4   +1.1                                5     2-mercapto butyryl carnitine Cl                                                                 15 mg oral                                                                           +0.5   +0.9   +2.3                                5     4-mercapto butyryl carnitine Cl                                                                 20 mg oral                                                                           +0.4   +0.6   +1.2                                5     5-mercapto valeryl carnitine Cl                                                                 15 mg oral                                                                           +0.6   -0.3   +1.4                                __________________________________________________________________________

                  TABLE V                                                          ______________________________________                                         Mucolytic activity in vitro of compounds of general formula (I)                and acetylcysteine; modifications of human sputum density                                       Percentage drop ± s.e. of                                                   the tracing versus maximum                                                     peak (*) after addition of 1                                                   ml of a 10% solution of the                                                    test compounds at the                                                          dilutions indicated                                           Compounds          1/30       1/60                                             ______________________________________                                         mercapto acetyl carnitine Cl                                                                      78.3 ± 5                                                                               45.2 ± 4                                      2-mercapto propionyl carnitine Cl                                                                 85.4 ± 6                                                                               46.5 ± 6                                      3-mercapto propionyl carnitine Cl                                                                 87.9 ± 7                                                                               48.2 ± 5                                      2-mercapto butyryl carnitine Cl                                                                   85.3 ± 4                                                                               38.4 ± 5                                      4-mercapto butyryl carnitine Cl                                                                   92.5 ± 7                                                                               45.8 ± 4                                      5-mercapto valeryl carnitine Cl                                                                   90.3 ± 6                                                                               48.3 ± 6                                      Acetylcysteine     75.7 ± 7                                                                               22.3 ± 4                                      ______________________________________                                          (*) Mucolytic activity index                                             

As experimentally shown, the compounds of this invention significantly modify the rheological properties of sputum. On perusal of the obtained results a decrease in sputum density at the larger doses (or lower dilutions) and at the smaller doses (or higher dilutions) constantly higher than that provoked by acetylcysteine, is detected. On the other hand no one of the compounds increases bronchial secretion nor is able to block the ciliary movement of the epithelium of trachea ring preparations in time intervals shorter than those permitted.

Effect on Ciliary Activity

The ability of the compounds of formula (I) to affect the ciliary motility was studied by observing with the microscope the ciliary movement of rat trachea rings soaked in solutions of the test compounds.

By this technique it is possible to study, with relation to compound concentration and contact time, the ciliary movement block provoked by the tests compounds, which is related to mucus clearance from ciliary epithelium.

Substances to be used in the form of solutions must allow the foregoing block not to take place in less than fifteen minutes from contact.

2% aqueous solutions of the compounds of formula (I) provoked the ciliary movement block to take place in 18-20 minutes.

The compounds of the present invention are therapeutically useful for the treatment of burns and diseases of epithelia, for the treatment of the diseases of the respiratory tract and generally whenever it is important to restore to normal the metabolic cellular equilibrium of epithelia unbalanced by exogenous and endogenous factors. The patients in need thereof will be orally or parenterally administered a therapeutically effective amount of a mercapto acyl-carnitine of general formula (I).

The dose of mercapto acyl-carnitine of general formula (I) orally or parenterally administered will be generally comprised between about 2 and about 20 mg/Kg of body weight/day, although larger or smaller doses can be administered by the attending physician having regard to the age, weight and general conditions of the patient, utilizing sound professional judgement.

In practice, the mercapto acyl-carnitines are orally or parenterally administered in any of the usual pharmaceutical forms which are prepared by conventional procedures well-known to those persons skilled in the pharmaceutical technology. These forms include solid and liquid oral unit dosage forms such as tablets, capsules, solutions, syrups and the like as well as injectable forms, such as sterile solutions for ampoules and phials. The pharmaceutical composition can be in unit dosage form comprising from about 25 to about 1000 mg of a mercapto acyl carnitine of formula I. 

What is claimed is:
 1. Mercapto acyl-carnitines of the general formula ##STR43## wherein: X⁻ is a pharmacologically acceptable halogenide ion, andR is the mercapto acyl radical of a mercapto alkanoic acid having from 2 to 10 carbon atoms.
 2. As mercapto acyl-carnitine of claim 1, mercapto acetyl-carnitine hydrochloride.
 3. As mercapto acyl-carnitine of claim 1, 2-mercapto propionyl carnitine hydrochloride.
 4. As mercapto acyl-carnitine of claim 1, 3-mercapto propionyl carnitine hydrochloride.
 5. As mercapto acyl-carnitine of claim 1, 2-mercapto butyryl carnitine hydrochloride.
 6. As mercapto acyl-carnitine of claim 1, 3-mercapto butyryl carnitine hydrochloride.
 7. As mercapto acyl-carnitine of claim 1, 4-mercapto butyryl carnitine hydrochloride.
 8. As mercapto acyl-carnitine of claim 1, 5-mercapto valeryl carnitine hydrochloride.
 9. An orally or parenterally administrable pharmaceutical composition, for treating burns and as a mucolytic agent, which comprises:(a) a therapeutically effective amount of mercapto acyl-carnitine of general formula (I) ##STR44## wherein X⁻ is a pharmaceutically acceptable halogenide ion andR is the mercapto acyl radical of a mercapto alkanoic acid having from 2 to 10 carbon atoms, and (b) a pharmaceutically acceptable excipient.
 10. The pharmaceutical composition of claim 9 in unit dosage form characterized in that it comprises from about 25 to about 1000 mg of a mercapto acyl-carnitine of formula (I).
 11. A composition according to claim 9 wherein X⁻ is a chloride ion. 